In conventional methods for producing semiconductor devices provided with electrode plates on both sides of a power device (semiconductor device), electrode plates were bonded to both sides of the power device to form a composite body, after which this composite body was sealed with a thermosetting resin such as an epoxy resin (resin sealing step).
Thermosetting resins such as epoxy resins have such characteristics as cure shrinkage where they undergo volumetric shrinkage due to a bridging reaction when hardening at a high temperature, and heat shrinkage where they undergo volumetric shrinkage when cooled from a high-temperature state.
In a semiconductor device provided with electrode plates on both sides of a power device, the two electrode plates provided on both sides of the power device are separated a certain distance away from each other, with the power device, an electrode plate block and the like being provided between the electrode plates. In the resin sealing step mentioned above, the space between these two electrode plates was sealed with a thermosetting resin (hereinafter referred to as sealing resin). However, when the sealing resin injected between the two electrode plates undergoes shrinkage due to cure shrinkage or heat shrinkage, the two electrode plates try to approach closer to each other, while the power device, electrode plate block and the like come in their way. This may result in stress applied to the bonded portion between the sealing resin and electrode plates to cause separation, which may eventually lead to separation of the sealing resin and electrode plates when the bond strength between the sealing resin and electrode plates is overcome by this stress, whereby reliability of the semiconductor device may be reduced.
Similarly, there is a possibility that reliability of the semiconductor device may be reduced because of the sealing resin and electrode plates separating from each other in thermal cycles under a usage environment of the semiconductor device.
Accordingly, Patent Document 1 discloses a technique wherein a coating of resin such as polyamide resin or polyimide resin is applied between the sealing resin and electrode plates to enhance intimate contact between the sealing resin and electrode plates and to improve reliability of the semiconductor device.